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exam 3: chapter 9- cell communicaton

Terms in this set (59)

communication between cells
intercellular signaling
communication within cells
intracellular signaling
signaling release chemical signals in the form of a small molecule known as
ligands
small signaling molecules that bind to specific molecules thus delivering the signal in the process
ligands
ligands mainy interact with target cells proteins called
receptors
specific ligands with interact with
specific receptors
move by diffusion through extracellular matrix, examples include synaptic signals and neurotransmitters
paracrine signaling
signals from distant cells, typically produce a slower response with a long lasting effect (ex. hormones)
endocrine signaling
signaling cells that can also bind to the ligand that is released, such that signal and target cell can be the same or similar to each other (cell death signaling)
autocrine signaling
intracellular mediators that allow small signaling molecules to move between cells
direct signaling across gap junctions
in direct signaling across gap junctions, they have channels that are fluid filled. what does this allow?
it allows small signaling molecules-intracellular mediators to diffuse between two cells (ex. ca2+ are able to move in between cells but large molecules like proteins and DNA cannot
what does communication of direct signaling in gap junctions allow for?
it enables to communicate the current affairs of the cells that is next to the other target cell, thus allowing a group of cells to coordinate their response to a signal
4 categories of signaling
paracrine signaling involves a nerve cell. what does a nerve cell consist of?
- cell body
- dendrites
- axon
in an example of paracrine signaling, the distance between the presynaptic and postsynaptic cell is called the synaptic gap. what does it allow?
it is very small and allows for rapid diffusion of the neurotransmitter. enzymes in the synaptic cleft degrade some types of neurotransmitters to terminate the signal
travels between the nerve cells (paracrine signaling)
synaptic signal
what are the two types of receptors?
Intracellular receptor and cell surface receptor
describe internal receptors
- intracellular or cytoplasmic
- found in cytoplasm
- respond to hydrophobic molecules
- once inside cells, molecules bind to proteins that acts as regulators of mRNA synthesis (transcription) initiating the gene expression
- influence gene expression without to pass the signal on to other receptors/messengers
hydrophobic signaling molecules typically diffuse across the plasma membrane and interact with
intracellular receptors in the cytoplasm. many intracellular receptors are transcription factors that interact with DNA in the nucleus and regulate gene expression
describe cell surface receptors
- transmembrane receptors
- cell surface, membrane anchored proteins that bind to external ligand molecules
- spans throughout plasma membrane
- performs signal transduction
- specific to individual cell types
- 3 categories (ion channel linked, g protein linked, enzyme linked)
describe ion channel- linked receptor
these cell surface receptors bind a ligand and open the channel allowing specific ions to pass through. many aa in membrane region are hydrophobic but inside the receptor are hydrophilic to allow the passage of ions/water
when ligands bind, protein structure is changed allowing (ion channel- linked receptor)
ions to move in/out
describe G protein-linked receptor
- binds a ligand and activates G protein
- g protein then interacts w either an ion channel or an enzyme
- g proteins have 7 transmembrane domains but each has its own specific domain and binding site
- cell signaling is a cyclic event releasing GDP and picks up GTP
describe enzyme-linked receptor
- cell surface with intracellular domains associated with an enzyme
- tyrosine kinase is an enzyme linked receptor with a single transmembrane region, and extracellular and intracellular domains
explain the role of tyrosine kinase as enzyme linked receptor
- binding of a signaling molecule to the extracellular domain causes the receptor to dimerize
- tyrosine residues on the intracellular domain are then autophoshorylated triggering a downstream cellular response
- the signal is terminated by a phosphatase that removes the phosphates from the phosphotyrosine residues
- produced by signaling molecules and binds to receptors in target cells
- ligands acts chemical signals traveling to target cells
signaling moelcules
- steroid hormones have similar chemical structures to their precursor, cholesterol
- can diffuse directly across the plasma membrane into the cell where they interact with internal receptors
small hydrophobic ligands
- polar
- cant pass through membrane easily
- sometimes too large to pass through
- most of them binds to extracellular domain of cell surface receptors
- very diverse including small molecules, peptides and proteins
water soluble ligands
when a ligand binds to a receptor and the signal is transmitted through a cell membrane and into the cytoplasm continuing the signal (ocurrs only with cell receptors)
signal transduction
two receptors bind to each other to from a stable complex (binding of the ligands
- dimer (chemical comp when 2 molecules join together)
dimerization
chain of events including second messengers, enzymes and activated proteins that follow ligand binding to a receptor
signaling pathway
signals from two or more different cell-surface receptors merge to activate the same response in the cell
signal integration
exaplain how EGRF is a signaling pathway
- the epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase involved in the regulation of cell growth, wound healing, and tissue repair
when EGF binds to the EGFR, a cascade of downstream events causes the cell to grow and divide
if EGFR is activate at inappropriate times,
uncontrolled cell growth (cancer) may occur
what is a possible result of a mutation in a kinase that controls a pathway that stimulates cell growth?
if a kinase is mutated so that it is always activated, it will continuously signal through the pathway and lead to uncontrolled grow and possible cancer. if a kinase is mutated so that it can't function, the cell will not respond to ligand bonding
the induction of a pathway depends on
the modification of cellular component by an enzyme
during intracellular signaling, one method is phosphorylation. what happens here?
a phosphate group (PO4-3) is added to residues of the amino acids serine, threonine, and tyrosine
the enzyme that catalyzes the transfer of a phosphate group
kinase
what is the role of second messengers? (intracellular signaling)
- small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor
- help spread a signal through cytoplasm by altering certain cellular proteins
explain how cAMP is a second messenger
it serves as a second messenger to activate or inactivate proteins within the cell. termination of the signal occurs when an enzyme called phosphodiesterase converts cAMP into AMP
the enzyme phospholipase C breaks down PIP2 into what two things?
IPS and DAG both which serve as second messengers
a MAP kinase that activates translation when it is phosphorylated
ERK
what does ERK phosphorylate?
MNK1
what does MNK1 phosphorylate?
eIF-4E
when eIF-4E becomes phosphorylated, the mRNA unfolds allowing
protein synthesis in nucleus to begin
in response to cell signaling, there is an increase in
cell metabolism
how does cell metabolism occur?
adrenaline activates b-adrenergic receptors which increase cAMP. cAMP activates PKA. PKA phosphorylates two enzymes which lead to a ready supply of glucose and an increase in metabolism
in response to cell signaling, cell growth occurs. how?
- growth factors bind to tyrosine kinases
- this initiates a pathway which activates MAP kinase pathway
- MAP kinase stimulates protein expression that leads to cell division
cell death
apoptosis
cell signals are terminated by
degradation of ligands or by other signals
enzymes that remove the phosphate group attached to proteins by kinases
phasphatases (ex. of cell death)
how do yeast cells communicate?
- they release a signaling molecule called mating factor
- mating factor binds to cell-surface receptors in nearby yeast cells
- they stop their normal growth cycles and initiate a cell signaling cascade that includes protein kinases and GTP- binding proteins are are similar to G-proteins
in bacteria, what is the key factor for signaling?
population density
what is bacterial signaling called?
quorum sensing
- it utilizes molecules called autoinducers
The secretion of hormones by the pituitary gland is an example of
Endocrine signaling
What property enables the residues of the amino acids serine, threonine, and tyrosine to be phosphorylated?
They contain a hydroxyl group.
Why are ion channels necessary to transport ions into or out of a cell?
Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane
What property prevents the ligands of cell-surface receptors from entering the cell?
The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
What is the function of a phosphatase?
A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.
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